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Oct-2005

Optimising FCC profitability

Additives have helped a Chinese refinery to yield increased profitability of over $3 million a year by transforming low-valued slurry into high-valued gasoline

Xia Rong’an, Liu Huaiyuan, Wu Kai and Guo Jian, PetroChina Corporation Lanzhou Petrochemical Company
David He and Solly Ismail, BASF Catalysts

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Article Summary

Highly profitable fluid catalytic cracking (FCC) operations are capable of processing a wide range of feedstocks without sacrificing the rate of feed to the FCC unit. However, many bottlenecks prevent the refiner from processing a wider range of feedstocks under varying processing conditions. Linear programming studies indicate that the optimal operational point for a FCC unit is when it is operating against the maximum number of bottlenecks available. Some of these are located in the reactor-regeneration system, while others may be downstream in the recovery section. Examples of frequently observed bottlenecks include:
• Wet gas compressor
• Air blower
• Metallurgical limit of the regenerator
• Catalyst circulation
• Main fractionator overhead system
• Downstream recovery system.

Refiners are aware of the financial benefits of operational flexibility, but complex cost considerations, an uncertain future profit picture and potential operational issues combine to make it difficult to over-invest for contingencies during the design stage of the unit. To address some of these shortcomings, refiners have periodically resorted to making modifications on an ad-hoc basis during turnarounds, long after the plant has been constructed. Examples of evolutionary changes to improve FCC unit profitability include:
• Changing the riser configuration to improve product selectivity
• Installation of rapidly disengaging devices to prevent over-cracking or unwanted side reactions
• The inclusion of improved feed-injection devices.

Whether a refiner wants to improve their existing operation beyond a constraint or get more performance out of installed capital upgrades, FCC additives are a rapid and cost-effective option. For example, Engelhard’s proprietary Converter additive has been used successfully in several commercial operations to facilitate such changes and improve profitability. At Petro-China’s Lanzhou refinery, this type of additive solution yielded increased profitability of more than $3 million (26.7 million Yuan) annually.

The approach used by the PetroChina Lanzhou refinery was both conservative and conventional; the company did not want to evaluate an experimental product. It needed to be convinced that the conversion-enhancement additive would create value and wanted to see real commercial data from other FCC customers.

Why additives?
Engineers are very comfortable with the use of additives in FCC units; they have been successfully used in operations to improve refinery profitability for more than 20 years. However, more recently, refiners have embraced the concept of conversion-enhancement additives to provide them with a new degree of freedom or functional capability to further optimise their operations. This low-cost, low-risk option is ideal for refineries wanting to increase unit profitability. The reasons for FCC additives meeting the high-return, low-risk criteria are:
• Proven commercial experience
• Quick to implement and verify
• No adverse operational risk
• Virtually no capital expenditure.

This is why over two dozen FCC units in several countries have successfully applied Converter additive to improve unit profitability. This additive has been used in operating conditions covering an extensive range of feedstocks, and in FCC units processing high-quality, clean vacuum gas oils with a low metals content. It has also been utilised successfully with feedstock mixtures containing varying degrees of resid with high levels of nickel and vanadium.

Refiners can verify the benefits of conversion-enhancement additives quicker than they can a catalyst change. When a new catalyst is to be implemented, the performance and benefits are not fully realised until an inventory changeover of approximately 70% has occurred. However, Converter’s results can be seen when the additive level has reached a mere 10%, giving refiners a new degree of freedom to trim or further optimise their activity levels of base catalyst.

While most refiners opted to gradually increase the concentrations of Converter in their inventory, the PetroChina Lanzhou refinery base-loaded the additive and so was able to see the beneficial results of the change earlier.

Conversion-enhancement additives have the same physical properties as the base catalyst supplied by all reputable catalyst technology suppliers and will not have a negative effect on the catalyst, such as a reduction in the catalyst circulation capability of the unit, increased attrition or lower metals tolerances. Other than the physical properties, which are almost identical to a regular FCC catalyst, the additive’s key attribute is to provide additional selective conversion-enhancement characteristics. In the case of PetroChina Lanzhou, this allowed the engineers to optimise the selective activity of the catalyst to more closely match the needs of the refinery’s current operating conditions and objectives.

What makes conversion-enhancement additives particularly attractive is that they require virtually no capital investment. They can be preblended with regular FCC catalysts, added separately with a loader, or simply added with the use of a day tank. Refiners are keenly aware that even small plant modifications can cost millions, so the lowest capital-intensive option is always welcomed.

In the case of PetroChina Lanzhou, no additional capital investment was required and all desired goals were achieved.


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